This invention relates to a lubrication system and in particular, although not exclusively, to a lubrication system for a gear unit, and a gear unit comprising a lubrication system, wherein said gear unit comprises a plurality of rotatable components rotatably supported by rotary shaft bearings such as ball bearings or roller bearings.
In a gear unit, as well as other types of lubricated equipment, the cleanliness of the oil is one of the most important factors influencing the life time of the bearings. In a method of bearing calculation according to ISO 281 standard, and in combination with a service life factor (axyz) dependent on load and contamination, the factor for the contamination varies from 0 to 1. For dip or splash lubricated gear units, the factor can never become 1 because there is no possibility of effective filtration. In the case of force lubricated gear units using a filter to improve cleanliness and reduce the contamination, significant expense is involved because micro filters must be used to get a good contamination factor approaching 1.
In contaminated oil it is primarily only hard particles that decrease the working life of the bearing. Normally those particles are of steel and arise from wear occurring during use. It is known to employ oil sump drain plugs of the kind incorporating a magnet to collect such particles, but generally these are of only poor effectiveness because the magnet is of only small size.